A pictorial showing bark and wood layer of a mature stem which further disintegrated into xylem (Sapwood), xylem (Heartwood), vascular cambium, phloem, cork cambium and cork.

FIGURE 23–14 Formation of Wood and Bark This diagram shows the layers of wood and bark in a mature tree that has undergone several years of secondary growth. Classify Which two tissues are meristems?

d

Formation of Bark In a mature stem, all of the tissues found outside the vascular cambium make up the bark, as shown in Figure 23–14. These tissues include phloem, the cork cambium, and cork. As a tree expands in width, the phloem layer must grow as well. This expansion may cause the oldest tissues to split and fragment as the expanding stem stretches them. The cork cambium surrounds the cortex and produces a thick, protective layer of waterproof cork that prevents the loss of water from the stem. As the stem increases in size, outer layers of dead bark often crack and flake off the tree.

23.3 Assessment

Review Key Concepts

    1. Review What are three important functions of stems?

    2. Explain How does the arrangement of vascular bundles in monocot stems differ from that of dicot stems?

    3. Apply Concepts How do the functions of a stem relate to the functions of the roots and leaves of a plant?

    1. Review Define primary and secondary growth.

    2. Explain Which meristem is involved in primary growth? Which are involved in secondary growth? Explain their roles.

    3. Predict Describe what would happen over time to a tree sapling that could grow only taller, not wider.

WRITE ABOUT SCIENCE

Creative Writing

  1. Pretend that you are small enough to enter a dicot plant through its root system. Describe what you would see as you traveled into a plant and through one of its stems. Include illustrations to enhance your description. Hint: Review the illustrations in this chapter for ideas.

End ofPage 679

Table of Contents

Miller & Levine Biology
About the Authors
Changing the World of Biology Education
Contents
Diversity of Life: A Visual Guide DOL•1–DOL•64
Labs and Activities
Features
UNIT 1 The Nature of Life
1 The Science of Biology
2 The Chemistry of Life
Unit Project
UNIT 2 Ecology
3 The Biosphere
4 Ecosystems and Communities
5 Populations
6 Humans in the Biosphere
Unit Project
UNIT 3 Cells
7 Cell Structure and Function
8 Photosynthesis
9 Cellular Respiration and Fermentation
10 Cell Growth and Division
Unit Project
UNIT 4 Genetics
11 Introduction to Genetics
12 DNA
13 RNA and Protein Synthesis
14 Human Heredity
15 Genetic Engineering
Unit Project
UNIT 5 Evolution
16 Darwin's Theory of Evolution
17 Evolution of Populations
18 Classification
19 History of Life
Unit Project
UNIT 6 From Microorganisms to Plants
20 Viruses and Prokaryotes
21 Protists and Fungi
22 Introduction to Plants
23 Plant Structure and Function
24 Plant Reproduction and Response
Unit Project
UNIT 7 Animals
25 Introduction to Animals
26 Animal Evolution and Diversity
27 Animal Systems I
28 Animal Systems II
29 Animal Behavior
Unit Project
UNIT 8 The Human Body
30 Digestive and Excretory Systems
31 Nervous System
32 Skeletal, Muscular, and Integumentary Systems
33 Circulatory and Respiratory Systems
34 Endocrine and Reproductive Systems
35 Immune System and Disease
Unit Project
A Visual Guide to The Diversity of Life
HOW TO USE THIS GUIDE
THE TREE OF LIFE
Bacteria
Protists
Fungi
Plants
Animals
Appendices
Appendix A Science Skills
Appendix B Lab Skills
Appendix C Technology & Design
Appendix D Math Skills
Appendix E Periodic Table
Glossary
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
Q, R
S
T
U
V
W
X, Y, Z
Index
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
Q
R
S
T
U
V
W
X
Y
Z
Credits
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